This invention is related to the testing of radio frequency chips and in particular to a method and apparatus for testing integrated circuits (xe2x80x9cchipsxe2x80x9d) that overcomes many of the disadvantages of the prior art.
Many companies are now producing radio frequency (RF) chips for use in wireless local area networks (WLANs) and other wireless applications. For these chips to be economically mass-produced, a testing apparatus and method are desired that do not require a high level of expertise to operate.
A typical test system tests a device, called that the xe2x80x9cdevice under testxe2x80x9d (DUT), e.g., an RF chip that has been mounted on a xe2x80x9cload board.xe2x80x9d A typical load board is a printed circuit board (PCB) that may be about 30 cm by 30 cm, and about 5 mm thick. The load board sits on top of a tester and includes a set of probes. The probes are connected to a set of instruments, including RF signal sources and measuring devices.
A conventional programmable electronic circuit test system, generally indicated by the numeral 110, is shown in FIG. 1. The electronic circuit tester 110 comprises a test head 112 electrically connected by cables routed through a conduit 114 to one or more rack(s) 116 of electronic test and measurement instruments, such as ac and dc electrical signal generators for applying electrical signals to a device or integrated circuit interfaced to the test head, and signal analyzers, for example, an oscilloscope and a network analyzer, for measuring the response(s) to those applied electrical signals. As shown in FIG. 1, the test head 112 interfaces to the DUT 120 via a load board 118 connected to the cables in the conduit 114. The DUT 120 is connected to the load board via a socket. The configuration of the load board 118 depends on the type of DUT.
As shown in FIG. 1, the test head 112 is mounted on a dolly 122. Since the electronic circuit tester 10 can be employed to test both packaged devices and integrated circuits, as well as device or integrated circuit chips on wafer, the test head 112 is preferably mounted by pivotable connections 124 to the dolly 122. The pivotable connections 124 enable the test head 112 to be positioned in an approximately upward facing horizontal position so that the appropriate load board 118 can be mounted on the test head of the electronic circuit tester 110 by an operator.
For testing in a production environment, the instruments are programmed to carry out a set of tests automatically. Once the load board 118 is mounted, one DUT 120 after another is loaded into a matching socket on the load board 118, then unloaded, then a new DUT is loaded. The loading and unloading is carried out automatically by an automatic chip-handling machine (xe2x80x9chandlerxe2x80x9d), not shown in FIG. 1.
Because of the need to automatically load and unload the DUTs, in one embodiment, the DUT faces upwards where it is reachable by an automatic loader, while the RF connection to and from the tester, e.g., to provide RF signal to the load board or to accepting RF signals from the load board, are on the opposite side of the load board than is the DUT. The load board therefore has to carry RF signals to and from one side of the board from and to the other. In the prior art, for frequencies up to about a GHz or two, connectors are used that pass through the load board. FIG. 2 shows one such prior art connector 203 passing through a section 205 of a load board.
For applications such as WLANs, the range of frequencies of interest may be in the multi-GHz range. The IEEE 802.11a standard, for example, uses several frequencies between 5.0 and 5.8 GHz. Accurately coupling the DUT 120 and load board 118 to the tester normally requires matching to the particular frequency of a test. Such matching might require additional circuitry, e.g., such microwave passive components as microwave capacitors, and so forth.
The prior art method of passing RF signals from one side of the board to the other side is not suitable for frequencies in the range of 5 GHz or higher. When connector 203 passes through the load board section 205, there is a 90-degree connection 207 at the top (IC) side of the load board. Such a bend causes mismatch problems at frequencies in the range of 5 GHz or higher. Boards that are 5 mm thick as load boards can be may start having problems at frequencies as low as 1 GHz.
Furthermore, the tuning for one frequency, e.g., one frequency channel of a WLAN, may not be applicable to any other frequency. A skilled engineer therefore typically carries out tuning. Such is clearly not amenable to a mass production environment.
There thus is a need for an apparatus and test method that avoids re-tuning, can test multiple frequencies in the multi-GHz range without requiring re-calibration, is easily reproduced in the field, and is operable by a low-skilled operator.
Disclosed herein is load board for connecting an RF integrated circuit device (the DUT) to a tester for testing. The load board includes a PCB having a DUT side and a non-DUT side. The DUT is insertable to a socket on the DUT side. The non-DUT side is accessible to one or more RF connectors to which an RF cable is connectable. Each RF connector provides an RF connection to a tester. The PCB includes at least one aperture through which a coaxial connection may be made to a cable connected to one of the RF connectors. Each coaxial connection through each aperture is electrically coupled on the DUT side to the DUT socket and matched for a range of frequencies up to at least approximately 5 GHz, including the frequencies used in the IEEE 802.11a standard.
One embodiment of the load board has an end launch connector on one edge of each aperture that has a coaxial connection. Each end launch connector is electrically connected to the socket and matched for the range of frequencies up to at least 5.8 GHz, such that the coaxial connection through each aperture is via the end launch connector at the edge of the aperture.
Also disclosed is a method for connecting radio frequency signals from the DUT side to the non-DUT side of a load board. The board including a socket on the DUT side into which the DUT is insertable. The method includes providing at least one aperture on the board, making a coaxial connection from the DUT side to the non-DUT side of the board though the aperture, electrically coupling the DUT side of the coaxial connection with the socket, and matching the coaxial connection for a range of frequencies up to at least approximately 5 GHz, including the frequencies of the IEEE 802.11a standard. The non-DUT side of the coaxial connection is accessible to one of a set of one or more RF connectors onto which an RF cable is connectable. Each such RF connector providing an RF connection to the tester such that RF signals in the range of frequencies can be input to or output from the tester from or to a DUT inserted in the socket.
One embodiment of the method includes mounting an end launch connector on an edge of each aperture through which there is a coaxial connection. Each end launch connector is electrically coupled to the socket and matched for the range of frequencies up to at least 5.8 GHz, so that the electrical coupling on the DUT side of the coaxial connection with the socket is via the end launch connector at the edge of the aperture.